Methamphetamine (Meth) is a major risk factor in the epidemiology of HIV, promoting behavior that both increases exposure to virus and reduces adherence to treatment. But beyond such effects on behavior, Meth appears to augment HIV replication and accelerate progression to AIDS. We hypothesize that this drug of abuse can act as a potent facilitator of HIV infection and transmission by disabling specific components of host intracellular defense. This hypothesis is based on our recent findings that Meth markedly decreased expression of cellular proteins that oppose HIV, specifically the RNA-induced silencing complex (RISC) component, Argonaute-1 (AGO1), which mediates miRNA processing and function, and the P-body constituent, APOBEC3G. In addition, Meth reduced miRNA species in CD4+ T-cells that regulate host molecules PCAF and Pur-a, and are known to restrict HIV replication. To our knowledge, there are no previous reports of these effects of Meth on intracellular mediators that limit HIV replication and transmission. We will pursue this new paradigm of Meth disarming specific intracellular defenses and enhancing HIV in a series of aims outlined below. Specific points of innovation include: (1) exploring unique effects of Meth on the RISC component AGO1 which opposes HIV; (2) understanding how Meth can regulate miRNAs, and cellular HIV dependency factors, focusing on PCAF and Pur-a; (3) characterizing effects of Meth on the actin cytoskeleton in dendritic cells and macrophages, so that instead of virus degradation in lysosomes, HIV is trafficked to exosomes and more readily transmitted at the immune synapse to CD4+ T-cells. Building on our novel preliminary data, we will pursue experimentally the following specific aims: (1) Characterize the molecular mechanisms whereby Meth can reduce AGO-1 expression and function, and cooperate with HIV-1 in altering the structural integrity of P-bodies. (2) Further characterize changes in cellular miRNA species that are differentially modulated by Meth, and how these changes augment HIV-1 replication. (3) Characterize effects of Meth on the actin cytoskeleton and lamellipoda formation in dendritic cells, focusing on trafficking of the RISC and associated miRNA to P-bodies, and shunting of HIV to an exosome pathway rather than to lysosomal degradation. By further generating this new knowledge, we hope to provide the foundation for innovative strategies to limit HIV infection in users of Meth, a prominent risk factor for AIDS.